The human body functions through a number of interdependent physiological systems controlled through various mechanical, electrical, and chemical processes. The metabolic state of the body is constantly changing. For example, as exercise level increases, the body consumes more oxygen and gives off more carbon dioxide. The cardiac and pulmonary systems maintain appropriate blood gas levels by making adjustments that bring more oxygen into the system and dispel more carbon dioxide. The cardiovascular system transports blood gases to and from the body tissues. The respiratory system, through the breathing mechanism, performs the function of exchanging these gases with the external environment. Together, the cardiac and respiratory systems form a larger anatomical and functional unit denoted the cardiopulmonary system.
Various disorders may affect the cardiovascular, respiratory, and other physiological systems. For example, heart failure is a clinical syndrome that impacts a number of physiological processes. Heart failure is an abnormality of cardiac function that causes cardiac output to fall below a level adequate to meet the metabolic demand of peripheral tissues and internal organs. Heart failure is often referred to as congestive heart failure (CHF) due to the accompanying venous and pulmonary congestion. Congestive heart failure may have a variety of underlying causes, including ischemic heart disease (coronary artery disease), hypertension (high blood pressure), and diabetes, among others.
There are a number of diseases and disorders that primarily affect respiration, but also impact other physiological systems. Emphysema and chronic bronchitis are grouped together and are known as chronic obstructive pulmonary disease (COPD). Pulmonary system disease also includes tuberculosis, sarcoidosis, lung cancer, occupation-related lung disease, bacterial and viral infections, and other conditions.
Chronic obstructive pulmonary disease generally develops over many years, typically from exposure to cigarette smoke, pollution, or other irritants. Over time, the elasticity of the lung tissue is lost, and the lungs become distended, unable to expand and contract normally. As the disease progresses, breathing becomes labored, and the patient grows progressively weaker. Other types of non-rhythm related pulmonary diseases or disorders include restrictive pulmonary diseases, infections pulmonary diseases, diseases of the pleural cavity, and pulmonary vasculature, for example.
Breathing disorders include various forms of rhythm-related disorders such as sleep apnea and hypopnea, among other forms. Disordered breathing is a respiratory system condition that affects a significant percentage of patients between 30 and 60 years. Disordered breathing, including apnea and hypopnea, may be caused, for example, by an obstructed airway, or by derangement of the signals from the brain controlling respiration. Disordered breathing occurs when a patient experiences insufficient respiration with or without respiratory effort. Disordered breathing can originate from a deficiency in the central nervous system (central disordered breathing) or from an obstructed airway (obstructive disordered breathing). Lack of respiratory effort may result from a disruption of signals from the central nervous system to the respiratory muscles.
Central disordered breathing events are characterized by insufficient respiration and a concurrent lack of respiratory effort. Because the central nervous system signals that control breathing are interrupted, the patient's natural breathing reflex is not triggered. The patient makes no effort to breath or the respiratory effort is otherwise disrupted. Respiration ceases or is insufficient during the disordered breathing event.
An obstructive disordered breathing event may occur due to an obstruction of a patient's airway. For example, the patient's the tongue or other soft tissue of the throat may collapse into the patient's airway. The breathing reflex is triggered, but respiration is disrupted because of the occluded airway. Disordered breathing events may include central disordered breathing events, obstructive disordered breathing events, or mixed disordered breathing events that are a combination of obstructive and central types.
Sleep disordered breathing is particularly prevalent and is associated with excessive daytime sleepiness, systemic hypertension, increased risk of stroke, angina and myocardial infarction. Disordered breathing can be particularly serious for patients concurrently suffering from cardiovascular deficiencies.
Various types of disordered respiration have been identified, including, apnea (interrupted breathing), hypopnea (shallow breathing), tachypnea (rapid breathing), hyperpnea (heavy breathing), and dyspnea (labored breathing). Combinations of the respiratory cycles described above may be observed, including, for example, periodic breathing and Cheyne-Stokes respiration (CSR). Cheyne-Stokes respiration is particularly prevalent among heart failure patients, and may contribute to the progression of heart failure.
Because of the complex interactions between the cardiovascular, pulmonary, and other physiological systems as well as the need for early detection of various disorders, an effective approach to acquiring and organizing information related to respiratory events is desired. The present invention fulfills these and other needs, and addresses other deficiencies of prior art implementations and techniques